So a few months ago, after I received the classic plates for the '99, I decided that it's time to abandon the useless stock ECU completely and have the Megasquirt take over all controlling functions. A 'classic' car in PA doesn't require emissions testing and so I'm able to abandon the OBDII capability completely.
As we all know by now there's only one task the '99 stock ECU handles and that the MS3 can't do out of the box. That's the field control for the alternator. So I got one of Frank's boards to take care of this, running the same circuit as everybody else with an NB Miata and a Megasquirt. This worked great!
So then, in July, the makers of the MS come up with a new feature: Alternator field control for the Miata. Yippie! It's totally awesome too. You can do lots of things, like reducing the voltage during full-throttle operation, run the alternator a little harder during over-run cutoff, specify how long after a start it should be at charging voltage, also what that charging voltage is. And then, after a while it goes into battery maintenance mode. Great I think. This will give me more hp, better efficiency and longer battery life at the same time :-)
I load up the new firmware, do a little soldering on the MS, test it on my desk and everything seems to work. Install the bugger, drive around and it works great. Then I work on the '03 Miata and forget about the '99 for a while.
Then I install the roll-bar in the '99. It takes two guys approximately 6-8 hours. That 4-5 hours the manual specifies is total horse-crap. Driving home after the install the engine craps out on me. Looking at my laptop that is hooked up to the MS, I realize that the alternator isn't charging anymore.
Once I make it home, first I take apart the Megasquirt in order to find the problem. But that seems to work fine. Then I remove the alternator to have it checked out- Autozone does it for free. That seems to work fine too. So I look at the Megasquirt again. It works just the way it should.
Then I decide to check if the field-signal gets from the Megasquirt to the alternator and BINGO- no connection. I check again: no connection. I check the connectors at both ends: no problem.
So I decide to have a beer and then go ahead and run a new wire from the MS to the alt. While I'm drinking the beer I decide to check the schematic to look if there are any connectors in between that may have come lose.
And lo and behold there are two connectors. One is right after the Megasquirt, but the second connector is right at the passenger-side roll-bar support. Hmm. We disconnected a lot of stuff back there. So I removed a few covers etc. and sure enough- there is a connector that was not completely tight and the alternator field control is running right through it!
So now we're back to charging the battery. Yay!
Of course I will NEVER figure out, why Mazda is routing a signal from the ECU to behind the driver seat, behind the passenger seat, through the passenger side rear wheel well and then forward to the right side of the engine, where the alternator sits. What were the Mazda engineers smoking?
So children- don't be as stupid as I was: When you install your roll-bar, make sure you re-hook up ALL the connections back there.